Objective consists of the development of methods for the controlled enzymatic and chemical synthesis of large oligoribonucleotides of defined sequence. The strategy involves the use of enzymes, which have the capacity to form the internucleotide bond, with substrates that contain specific reversible chemical modifications. The particular enzymes to be exploited in the study are polynucleotide phosphorylase, RNA ligase, and terminal deoxyribonucleotidyl transferase.